The present invention relates to a blade tip clearance probe and a method for measuring blade tip clearance. More specifically, but without limitation, the present invention relates to a blade tip clearance probe that measures the gap between a blade tip and blade housing (or fan case) and a method for measuring blade tip clearance in an engine.
Gas turbine engines, steam turbines, aircraft engines, jet engines and other axial flow turbomachinery are typically designed to minimize the radial gap between a blade tip and a blade housing or fan case. Gaps between blade tips and fan cases (commonly referred to as blade tip gap) reduce efficiency by allowing gas or air to leak into the preceding stage of engine operation. The blade tip gap is a function of engine speed and temperature, and it changes during engine operation. High operating rotational speeds cause radial elastic growth in rotating hardware (i.e. blades), resulting in radial blade tip growth. High temperatures cause thermal expansion in the case and in the rotating hardware. A nondestructive inspection method of determining this gap at operating conditions is needed.
A thin metal rod can be used as a probe to measure the blade tip gap. The rod is inserted into an axially drilled bolt and fastened into place. The resulting assembly is then inserted into a mount plate attached to the fan case and the engine is operated for a specified time period. The amount of wear on the rod is recorded to determine the change in blade tip gap. The rods often bend or break which negates any data that was recorded. In addition, metal liberated from the rod, either as pieces or as powder can cause damage to the engine. Making these rods/probes is difficult and time consuming. Each probe must be custom made using a measurement of distance from the fan case boss to the blade tip. This introduces many errors such as measurement, data recording, and machining. Often the probes are made too short or too long. Short probes do not rub the blade tip, while long probes bend or break.
Engine testing, specifically aircraft engine testing, is very expensive and time schedules for testing are very tight. Performing multiple tests is often not an option. Many engine tests utilize electrical and/or laser equipment that is difficult to use and expensive to use and maintain.
For the foregoing reasons, there is a need for a new blade tip clearance probe and a method for measuring blade tip clearance. Information relevant to attempts to address these problems can be found in U.S. Pat. Nos. 5,017,796, 5,497,101, 5,760,593; and 5,739,524 (None of these patents are admitted to be prior art with respect to the present invention.) However, each of these references suffers from one of the above listed disadvantages.
The present invention is directed to a blade tip clearance probe and a method for measuring blade tip clearance that satisfies the needs listed above and below.
The present invention is directed to a blade tip clearance probe, which includes a rub probe support, a rub probe and an anti rotational lock. The rub probe support can be removably attached to a probe boss, which can be removably attached to a fan case or blade housing. The rub probe can be removably attached to the rub probe support. The rub probe is composed of soft composite material and is able to be threaded into the rub probe support. The anti rotational lock is able to lock the rub probe into place in the rub probe support and is able to prevent rub prove movement.
The present invention is also directed to a method for measuring blade tip clearance, which includes fastening a rub probe support to a probe boss attached to a fan case; threading a rub probe into the rub probe support until the rub probe contacts a blade tip in the fan case; backing the rub probe off a specified turn angle; operating an engine attached to the blade tip; and measuring wear on the rub probe.
It is an object of the invention to provide a blade tip clearance probe that is simple and inexpensive to manufacture, as well as easy to use. It is also an object of the invention to provide a blade tip clearance probe that does not need to be custom made. It is a further object of the invention to provide a blade tip clearance probe that can be produced in bulk and thus be more economical.
It is also an object of the invention to provide a blade tip clearance probe and method for measuring blade tip clearance that is non-destructive and safe. It is also an object of the present invention to provide a blade tip clearance probe and a method for measuring blade tip clearance that does not cause damage to the blade tips or the fan case. Since the rub probe is manufactured from soft composite material, it will not cause damage to the blade tips, the fan case or any other parts of the engine. The powder that is liberated from the rub probe during operation poses no damage risk to the engine.
It is also an object of the invention to provide a blade tip clearance probe and method for measuring blade tip clearance that is reliable and does not cause tolerances (an allowable variation in dimensions) to accumulate.